"up" is often an adverb or an adjective (and sometimes even a noun!), all cases where it should be capitalised. The same is true of "off" (often an adverb). So there's no good way to guess those, and defaulting to the standard upper case seems reasonable.
I'll venture a guess that the most common use of "cum" in English song titles is not as a preposition, but I'll admit I haven't checked.
All the rest are rare enough that they probably never got added to the guess case code. I honestly can't remember ever adding a track using "qua" to MusicBrainz, and the few ones I added with "per" and "re" were actually in Latin, except for "36 Mesostics re and not re Marcel Duchamp".